A common problem of real time image capturing systems (hereinafter referred to as “imaging systems”) is that images captured by such systems may contain motion artifacts due to movement of the image capturing device, or by movement of objects in a scene that is being captured. Both types of movements generally result in blurring of captured images. In order to produce high quality crisp still images, motion artifacts must be minimized.
Consider an imaging system as shown in FIG. 1 that supports both real time video and still image capture, i.e., a system that can process and send out either a single frame or multiple frames of images in real time. In such a system, image processing algorithms can be designed to process either a single frame or multiple frames. An advantage of such a system over a still image processing system is that image processing algorithms can take advantage of the correlation in adjacent frames so that better output quality can be produced.
U.S. Pat. No. 5,629,988 describes a method in video stabilization. Specifically, the method estimates a global motion vector between a captured image and a reference image, determines a transformation parameter based on the global motion vector, and applies the transformation to the captured image. U.S. Pat. No. 6,654,049 suggests using color values as a means to determine motion vector. U.S. Pat. No. 6,809,758 improves on the accuracy of global motion vector determination using a global motion vector histogram that is constructed from information in multiple frames. Since multiple frames are considered, the motion vector from frame to frame can follow a smooth trajectory and the result is improved.
The above methods rely on a global motion vector to correct for an image frame and would work well in video capture by reducing camera shake artifacts. However, these methods do not reduce motion artifacts due to object motion in a scene as object motion in a scene typically affects only a portion of the scene, and hence applying a global motion vector to the entire frame is generally not effective in such case.